5 solar masses is 1x10^34 g. 1 g of mass is roughly 0.9x10^14 J (mc^2).
So, roughly 1x10^48 J.
1 ly is roughly 1x10^16 m. Surface area of a sphere with r=1 ly, is 4πr^2 = 4π x 10^32 m^2 or roughly 1x10^33, so each m^2 of surface will receive 1x10^48/1x10^33 = 10^15 Watt, or about 10^12 x brighter than our Sun on Earth in sunny day, but for 1 second only.
2. Spacetime is 4d array: [x,y,z;t]. Warping of spacetime means that a scientist applies a mathematical formula to the array directly, like shader in OpenGL. It has no physical meaning. It just a quick way to simulate unknown physical process, to make a prediction.
3. No, it doesn't. Our local group of galaxies is expanding, but this is a coincidence. Actually, we are falling into a black hole. Nearest big black hole is in the center of our galaxy, then Great Attractor, then Shapley Attractor.